Optimization of electrochemical cell

ABSTRACT

A system and method for optimizing electrochemical cells including electrodes employing coordination compounds by mediating water content within a desired water content profile that includes sufficient coordinated water and reduces non-coordinated water below a desired target and with electrochemical cells including a coordination compound electrochemically active in one or more electrodes, with an improvement in electrochemical cell manufacture that relaxes standards for water content of electrochemical cells having one or more electrodes including one or more such transition metal cyanide coordination compounds.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Division of application Ser. No. 17/647,307 filedon Jan. 6, 2022; application Ser. No. 17/647,307 is a Continuation ofapplication Ser. No. 17/232,484 filed on Apr. 16, 2021; the contents ofwhich are all hereby expressly incorporated in their entireties byreference thereto, for all purposes.

FIELD OF THE INVENTION

The present invention relates generally to electrochemical cellsincluding a coordination compound electrochemically active in one ormore electrodes, and more specifically, but not exclusively, toimprovement in electrochemical cell manufacture by relaxing standardsfor water content of electrochemical cells having one or more electrodesincluding one or more transition metal cyanide coordination compounds.

BACKGROUND OF THE INVENTION

The subject matter discussed in the background section should not beassumed to be prior art merely as a result of its mention in thebackground section. Similarly, a problem mentioned in the backgroundsection or associated with the subject matter of the background sectionshould not be assumed to have been previously recognized in the priorart. The subject matter in the background section merely representsdifferent approaches, which in and of themselves may also be inventions.

Electrochemical cells are often characterized as using electrolytes thatfall into one of two classes: (i) aqueous electrolytes or (ii)non-aqueous electrolytes. Examples of the former include lead acid cellsand nickel/metal hydride cells. Examples of the latter includelithium-ion cells. It is well established that in cells containingnon-aqueous electrolytes, any trace water impurity, even at a lowconcentration of parts-per-million, will degrade the performance of thecell in one or more performance metrics. The solution is therefore toimplement additional costly and energy-intensive process steps such asvacuum-drying solid cell components, treating electrolytes orelectrolyte solvents with desiccants, and preventing re-uptake ofmoisture by maintaining rigorous dry room processes for all thesubsequent process steps including cell assembly. Electrode componentswill be dried as much as possible in an effort to remove as much tracewater as possible. This process adds to the complexity, risk, andresource costs in production of these cell stacks.

Regarding water content for non-aqueous electrolyte-containing cells,for example, see Reference [1]— Imhof, with FIG. 6 of Reference [1]illustrating that an increasing amount of ppm-level water impuritydecreases the reversibility of a charging/discharging process of agraphite electrode in a Li-ion cell. This is a conclusion of Reference[1] on page 1087: “experiments with EC/DMC-based electrolytes containingdifferent amounts of water have shown that the Li⁺ intercalation processbecomes less reversible as the water content increases.” (Referencesspecifically identified below and incorporated herein as noted.)

Some materials used as an electrode in an electrochemical cell mayinclude use of a transition metal cyanide coordination compound (TMCCC).In principle, electrochemical cells with TMCCC electrodes can bedesigned to use either aqueous or non-aqueous electrolytes. Aqueouselectrolytes would be preferred due to their low cost and superior ionicconductivity. However, using aqueous electrolytes makes it necessary tolimit the design to electrochemical cells with relatively low voltages,typically less than 1.5 V, in order to prevent the electrolyticdecomposition of water into hydrogen and oxygen. Therefore, reference[2] treats electrochemical cells using a TMCCC material as the positiveelectrode as belonging to the (ii) non-aqueous class. Reference [2]describes methods for drying TMCCC electrode materials to improve cellperformance. In particular, Reference [2] teaches a manganesehexacyanoferrate (MnHCF) TMCCC electrode material that is dried to a lowenough residual water content that all of the interstitial water isremoved. When this occurs, the MnHCF material undergoes a phasetransition from a cubic phase to a rhombohedral phase (column 8). Whenthis phase change occurs, all of the electrochemical capacity of theMnHCF electrode is captured in a single charge-discharge plateau. Havinga single reaction plateau is desirable because it allows anelectrochemical cell to be operated in a narrower voltage range,decreasing the cost and complexity of integrating the cell into otherelectronic systems. To achieve this result, Reference [2] furtherdescribes the use of a vacuum drying process in which the vacuumpressure is below 0.1 torr (column 7 and claim 1).

Reference [2] includes a TMCCC in which a range of water may be present(z in a range of 0 to 3.5). However, column 8 describes in detail thatall of the interstitial water must be removed from the structure toachieve the rhombohedral phase that has a single reaction plateau.Furthermore, in Reference [3] it is shown that the rhombohedral phasehaving a single reaction plateau is completely anhydrous. ThroughoutReference [3], the single plateau phase is referred to as “anhydrated”,as opposed to the “hydrated” phase having two reaction plateaus. FigureS2 is an idealized drawing of a unit cell, which cannot visualize thepresence of a few % of vacancies and H₂O associated with thesevacancies. The main manuscript includes elemental analysis results thatindicate Na_(1.89)Mn[Fe(CN)₆]_(0.97) 1.87H₂O before andNa_(1.89)Mn[Fe(CN)₆]_(0.97) 0.3H₂O after vacuum drying. Should thisanalysis method be 100% accurate, removing all non-coordinated but nocoordinated water should result in z=0.18 instead of z=0.3, however thissmall difference of 0.12 is believed attributable to measurement errors.Therefore, one of ordinary skill in the art would consider the teachingsof Reference [2] and Reference [3] to indicate that the rhombohedral,single-plateau phase is achieved when all of the water is removed fromthe structure, or in terms relevant to claim 1 of Reference [2], whenz=0.

Note that “anhydrated” as used in Reference [3] is not a commonly usedterm. It is usually defined as the anhydrous form of a material thattypically contains water. A reasonable interpretation of Reference [3]is that “anhydrated” is synonymous with “anhydrous”, meaning a substancethat contains no water or only a negligible quantity water as a traceimpurity. In contrast, had Reference [3] referred to the vacuum driedMnHCF as “dehydrated”, then it would be commonly understood that eithersome or all of the water initially present in the material had beenremoved.

In contrast to these disclosures, electrochemical cells that use TMCCCmaterials as an electrode may not exclusively fall into these aqueous ornon-aqueous classes, e.g., when one or more TMCCC electrodes with asubstantial water content are combined with a non-aqueous electrolyte.Optimization of operation of an electrochemical cell including TMCCCmaterials by managing the water content and assembly may be more complexthan heretofore appreciated by conventional battery manufacturingtechniques. For example, Reference [2] emphasizes on the advantage ofhaving the same electrochemical potential for oxidation/reduction of Mnand Fe sites. While having a wider capacity range within a narrowpotential range may seem attractive, no consideration of other batteryperformance criteria was made in Reference [2]. For example, Reference[2] does not mention whether any improvement of calendar or cycle lifecan be achieved with their anhydrous cathode material having arhombohedral crystal structure, nor whether their electrode material candeliver an acceptably high portion of its capacity within a narrowpotential window if it is discharged at any faster rate than the 10-hourdischarge shown in Reference [2], FIGS. 6B and 7A.

Commercialization costs for some electrochemical cell manufacturersinclude manufacture or purchases of electrolytes. The higher thestandard that is used for reducing water impurity levels in electrolyteshaving water, the greater the costs of those electrolytes which isdirectly related to consumer costs of completed cells, and thusultimately on the adoption of these types of electrochemical cells.

What may be beneficial is a system and method for optimizingelectrochemical cell manufacturing by reducing commercialization costs,including reduction of electrolyte costs used in their manufacturing.

BRIEF SUMMARY OF THE INVENTION

Disclosed is a system and method for optimizing electrochemical cellmanufacturing by reducing commercialization costs, including reductionof electrolyte costs used in their manufacturing. The following summaryof the invention is provided to facilitate an understanding of some ofthe technical features related to managing water content of electrolytesand of electrodes including TMCCC materials, and is not intended to be afull description of the present invention. A full appreciation of thevarious aspects of the invention can be gained by taking the entirespecification, claims, drawings, and abstract as a whole. The presentinvention is applicable to other electrochemically active compounds inaddition to TMCCC materials, particularly those that include waterdisposed in a crystal structure locations and water disposed in anon-coordinated manner.

Electrochemical cells in which energy storage is achieved by ionintercalation in transition metal cyanide coordination compounds (TMCCC)capable of co-intercalation of water have an advantage that the TMCCCmaterials may serve two important and concurrent/related functions: ionintercalation and removal of water from organic electrolytes. Partiallydehydrating TMCCC electrodes, e.g., by vacuum-drying, prior to cellassembly allows for a substantial relaxation of specifications for thenon-aqueous cell electrolyte regarding allowable concentration of waterimpurities. One reason is that the impurities will be absorbed, oncespecified correctly, into the TMCCC electrode material without anydisadvantage to cell performance and cycle life. And these substantiallyrelaxed specifications allow the material costs to be greatly reduced,further promoting use and development of these electrochemical materialsand systems.

An embodiment of the present invention includes electrode materials thathave a capacity to capture and release water within a total water budgetfor the electrodes that do not substantially degrade electrodeoperation. Contrary to what would be generally assumed by those skilledin the art, we found that many TMCCC materials require a substantialcontent of interstitial water in order to achieve optimal cellperformance, and that such interstitial water does not substantiallyaccelerate cell degradation when its amount is kept within anappropriate range. In contrast to a conventional view of a waterimpurity concentration that should be reduced as much as possible,electrochemical cells including an electrode having TMCCC activematerials maintain water within upper and lower bounds, with somebattery performance characteristics optimized at specified waterconcentrations.

An embodiment of the present invention includes removal of water fromsuch electrode materials prior to assembly of an electrochemical cell inwhich the electrode operates in an electrolyte containing water. Theelectrodes are prepared pre-assembly, e.g., dehydrating the electrodematerials to have a water content less than optimum, and then disposedin communication with a water-containing electrolyte having apre-assembly water content greater than what could be commerciallyobtained at greater cost. After assembly, the desiccating character ofthe electrode removes water from the electrolyte to move the electrodetowards more optimum operation while purifying the less-expensiveelectrolyte to produce a post-assembly electrochemical cell at loweroverall cost. The same endpoint could be achieved by tight specificationof the electrochemical components pre-assembly and implementingappropriate manufacturing facilities and conditions to maintain thesewater budgets so that the post-assembly specification is achieved.However, that latter process adds extra costs as compared to the use ofthe electrode as a desiccant.

An embodiment of the present invention may include improvedmanufacturing. As less aggressive water removal processes may berequired, some of the processing steps may be simplified. For example,an aspect of the present invention includes assembly of an entireelectrochemical cell, or a collection of such cells into a cell stack,one or more cells including at least one electrode with a TMCCC materialhaving a water content outside desired range(s), and then optimizing thewater in the assembled cell or cell stack. This is in contrast todehydrating/hydrating the individual materials and then assembling usingthe dehydrated/hydrated materials.

An embodiment of the present invention may include a method ofoptimizing cell performance including dehydrating/hydrating at least oneelectrode to a controlled residual water content that includes a lowerwater concentration than desired for post-assembly operation and anelectrolyte having a higher concentration of water than desiredpost-assembly (which reduces its cost for manufacture/purchase). Theprocess of assembly of an electrochemical cell with these components inthese states prior to the assembly allows the assembly process totransfer water from the electrolyte into one or more electrodes, whichlowers the post-assembly concentration of water in the electrolyte whileincreasing a water concentration in the electrodes. A characteristic ofTMCCC active materials in electrodes of electrochemical cells allows theincreased water concentration to not degrade or appreciably negativelyimpact the desired electrochemical properties of the electrodes.

An embodiment of the present invention may include a composition ofmatter of an electrochemical cell in which one or more electrodescontain a set nonzero amount of water wherein a specific amount of water(i.e., greater than zero and less than a threshold), distinguished fromelectrochemical cells with one or more electrodes containing TMCCCmaterials having an undefined n>0 amount of water. The electrodes andelectrolytes have a number of states including water concentrations foras-synthesized, pre-assembly (such as after partially drying thesynthesized materials, and post-assembly electrolytes and electrodes.

A method for producing an electrochemical cell having an electrodeconfigured to be disposed in communication with an electrolyte, mayinclude configuring a pre-installation electrode to include animpurity-absorbing material, the pre-installation electrode having aninitial set of electrical characteristics; and thereafter, communicatingthe pre-installation electrode with the electrolyte, the electrolyteincluding, prior to the communicating, an initial set of impurities at apre-installation concentration; and thereafter; absorbing, with thepre-installation electrode, an impurity from the initial set ofimpurities; wherein the absorbing step removes the impurity from theelectrolyte; and wherein the absorbing step configures, using theimpurity, the pre-installation electrode as a post-absorption electrode;and wherein the post-absorption electrode includes a post-absorption setof electrical characteristics greater than the initial set of electricalcharacteristics. This impurity may be water and the impurity-absorbingmaterial may include a TMCCC material in one or both of an anodeelectrode or a cathode electrode.

An electrochemical cell including a pre-communication electrolyte,including a pre-communication electrode including an impurity-absorbingmaterial, the pre-communication electrode having an initial set ofelectrical characteristics prior to a communication of thepre-communication electrode to the pre-communication electrolyte;wherein the pre-communication electrolyte, configured for thecommunication to the pre-communication electrode, includes an initialset of impurities at a pre-communication concentration prior to thecommunication of the pre-communication electrode to the pre-installationelectrolyte; and wherein the communication transfers an impurity fromthe initial set of impurities to the pre-communication electrodeproducing a post-absorption electrode; wherein the post-absorptionelectrode includes a post-absorption set of electrical characteristicsgreater than the initial set of electrical characteristics. The impuritymay include water and the impurity-absorbing material may include aTMCCC material.

An electrochemical cell including a cell stack having a liquidelectrolyte, an anode electrode, a separator, and a cathode electrode,the electrodes electrochemically communicated with the liquidelectrolyte, with the cell stack having an as-synthesized set ofproperties, a pre-communication set of properties before the electrodesare electrochemically communicated with the liquid electrolyte, and apost-communication set of properties after the electrodes areelectrochemically communicated with the liquid electrolyte; wherein theanode electrode and the cathode electrode each contain a transitionmetal cyanide coordination compound material having a compositionconforming to formula I, formula I includingA_(x)P_(y)[R(CN)₆]_(z)(H₂O)_(n); wherein A represents an alkali cationand P and R each represent a multivalent transition metal cation;wherein 0.5<z<1; wherein x, y, and z are related based on electricalneutrality, x>0, y>0, z>0; and wherein n=6*(1−z)+m_(k), with n>0, withk=0 to 4 identifying the as-synthesized material (k=0) and a set ofstates for the electrodes, and with 6*(1−z) associated with a quantityof coordinated water of the compound material, and with each m_(k)>0,each m_(k) associated with a quantity of interstitial water of thecompound material for one of the states of the electrodes, with eachsaid quantity m_(k) of interstitial water being equivalent to a weightpercentage M_(k)=m_(k)*W_(H2O)/W_(dry)*100%, with W_(H2O) being themolecular weight of water and W_(dry) being the molecular weight for thecomposition of formula I excluding all of its water content (orsubstantially all), with M₀ associated with an as-synthesized set ofproperties for said electrode, with M₁ associated with apre-communication set of properties for the anode electrode, with M₂associated with a pre-communication set of properties for the cathodeelectrode, with M₃ associated with a post-communication set ofproperties for the anode electrode, and with M₄ associated with apost-communication set of properties for the cathode electrode; andwherein the liquid electrolyte includes a polar organic solvent combinedwith an alkali metal salt and water having a water concentration, thewater concentration including a pre-communication water concentration c1and including a post-communication water concentration c2 and whereinc1>c2; wherein the as-synthesized set of properties includes M₀ up to45% for formula I materials; wherein the M₁ includes a range between 1%and 12% for formula I materials of the anode electrode with M₁≤M₃;wherein the M₂ includes a range between 1% and 12% for formula Imaterials of the cathode electrode with M₂≤M₄; and wherein M₃+M₄>M₁+M₂.Note that this 45% is based on an extreme end of atomic compositionswith z=0.5 and M_(k)=4.0, i.e., 2H₂O molecules per interstitial site.This value is 22.5% when the limit is set to M_(k)=2.0 instead. The drymolecular weight varies widely over the z range; for Na_(x)Mn^(II)_(1.0)[Mn^(II)(CN)₆]_(z) it is 160.5 g/mol at z=0.5 and 312 g/mol atz=1.0. This informs one of a meaningfulness of expressing M_(k) in dryweight %.

An electrochemical cell, including a cell stack having a liquidelectrolyte, an anode electrode, a separator, and a cathode electrode,the electrodes electrochemically communicated with the liquidelectrolyte, with components of the cell stack having an as-synthesizedset of properties, a pre-communication set of properties before theelectrodes are electrochemically communicated with the liquidelectrolyte, and a post-communication set of properties after theelectrodes are electrochemically communicated with the liquidelectrolyte; wherein a first particular one electrode of the electrodesincludes a transition metal cyanide coordination compound materialhaving a composition conforming to formula I, formula I includingAxPy[R(CN)6]z(H2O)n; wherein A represents an alkali cation and P and Reach represent a multivalent transition metal cation; wherein 0.5<z<1;wherein x, y, and z are related based on electrical neutrality, x>0,y>0, z>0; and wherein n=6*(1−z)+mk, with n>0, with k=0 identifying anas-synthesized material and k=1 to 2 identifying a set ofpost-synthesized states for the first particular one electrode, and with6*(1−z) identifying as a quantity of coordinated water of the compoundmaterial, and with each mk>0, each mk identifying as a quantity ofinterstitial water of the compound material for one of the states of thefirst particular one electrode, with each the quantity mk ofinterstitial water being equivalent to a weight percentageMk=mk*WH2O/Wdry*100%, with WH2O being the molecular weight of water andWdry being the molecular weight for the composition of formula Iexcluding all of its water content, with M0 identifying as anas-synthesized set of properties for the first particular one electrode,with M1 identifying as a pre-communication set of properties for thefirst one particular electrode, with M2 identifying as apost-communication set of properties for the first particular oneelectrode; and wherein the liquid electrolyte includes a polar organicsolvent combined with an alkali metal salt and water having a waterconcentration, the water concentration including a pre-communicationwater concentration c1 and including a post-communication waterconcentration c2 and wherein c1>c2; wherein the as-synthesized set ofproperties includes M0 up to 45% for a set of as-synthesized materials,the set of as-synthesized materials including the composition of FormulaI; wherein the M1 is less than about 12% for a set of electrodematerials of the first particular one electrode, the set of electrodematerials including the composition of Formula I; and wherein M2>M1.

An embodiment for the cell and the method may include c1<1,000 ppm andwith c2<100 ppm or c2<100, the polar organic solvent may include amononitrile (which may sometimes have the liquid electrolyte including adinitrile as an additive), the anode and cathode formula I materials maybe substantially the same or different, and permutations of values forM₁, M₂, M₃, and M₄ maintain the identified boundary conditions: M₁≤M₃,M₂≤M₄, and M₃+M₄>M₁+M₂. (e.g., M₁=M₃, M₂=M₄ or M₁<M₃ and M₂<M₄), andpermutations and combinations thereof.

A method for assembling an electrochemical cell, including a) assemblinga cell stack having a liquid electrolyte, an anode electrode, aseparator, and a cathode electrode, the electrodes electrochemicallycommunicated with the liquid electrolyte after the assembling step, withthe cell stack having an as-synthesized set of properties, apre-assembly set of properties before the electrodes areelectrochemically communicated with the liquid electrolyte, and apost-assembly set of properties after the electrodes areelectrochemically communicated with the liquid electrolyte; b)transferring water, responsive to the assembling step, from the liquidelectrode to at least one of the electrodes; and c) decreasing,responsive to the transferring water step, a concentration of water inthe liquid electrolyte; wherein the anode electrode and the cathodeelectrode each contain an active material including a transition metalcyanide coordination compound material having a composition conformingto formula I, formula I including A_(x)P_(y)[R(CN)₆]_(z)(H₂O)_(n);wherein A represents an alkali cation and P and R each represent amultivalent transition metal cation; wherein 0.5<z<1; and whereinn=6*(1−z)+m_(k), with n>0, with k=0 to 4 identifying the as-synthesizedmaterial (k=0) and a set of states for the electrodes, and with 6*(1−z)associated with a quantity of coordinated water of the compoundmaterial, and with each m_(k)>0, each m_(k) associated with a quantityof interstitial water of the compound material for one of the states ofthe electrodes, with each said quantity m_(k) of interstitial waterbeing equivalent to a weight percentageM_(k)=m_(k)*W_(H2O)/W_(dry)*100%, with W_(H2O) being the molecularweight of water and W_(dry) being the molecular weight for thecomposition of formula I excluding all of its water content (orsubstantially all), with M₀ associated with an as-synthesized set ofproperties for said electrode, with M₁ associated with the pre-assemblyset of properties for the anode electrode, with M₂ associated with thepre-assembly set of properties for the cathode electrode, with M₃associated with the post-assembly set of properties for the anodeelectrode, and with M₄ associated with the post-assembly set ofproperties for the cathode electrode; and wherein the liquid electrolyteincludes a polar organic solvent combined with an alkali metal salt andwater having a water concentration, the water concentration including apre-assembly water concentration c₁ and including a post-communicationwater concentration c2 and wherein c1>c2; wherein the as-synthesized setof properties includes M₀ up to 45% for formula I materials; wherein theM₁ includes a range between 1% and 12% for formula I materials of theanode electrode with M₁≤M₃; wherein the M₂ includes a range between 1%and 12% for formula I materials of the cathode electrode with M₂≤M₄; andwherein M₃+M₄>M₁+M₂.

A method for assembling an electrochemical cell, including assembling acell stack having a liquid electrolyte including a quantity ofelectrolytic water, an anode electrode, a separator, and a cathodeelectrode, the electrodes electrochemically communicated with the liquidelectrolyte during the assembling step, with the cell stack having anas-synthesized set of properties, a pre-assembly set of propertiesbefore the electrodes are electrochemically communicated with the liquidelectrolyte, and a post-communication set of properties after theelectrodes are electrochemically communicated with the liquidelectrolyte, wherein the sets of properties each include a waterconcentration of the electrolyte and a quantity of component water in acomponent coupled to the liquid electrolyte of the cell stack; coupling,during the assembling step, the liquid electrolyte to the component; andtransferring, during the coupling step, a post-assembly quantity ofelectrolytic water to the component water; and reducing, responsive tothe transferring step, the water concentration of the liquidelectrolyte.

A method for assembling an electrochemical cell, including: assembling acell stack having a liquid electrolyte including a quantity ofelectrolytic water, an anode electrode, a separator, and a cathodeelectrode, the electrodes electrochemically communicated with the liquidelectrolyte during the assembling step, with the cell stack having anas-synthesized set of properties, a pre-assembly set of propertiesbefore the electrodes are electrochemically communicated with the liquidelectrolyte, and a post-communication set of properties after theelectrodes are electrochemically communicated with the liquidelectrolyte, wherein the sets of properties each include a waterconcentration of the electrolyte and a quantity of component water in acomponent coupled to the liquid electrolyte of the cell stack; coupling,during the assembling step, the liquid electrolyte to the component; andtransferring, during the coupling step, a post-assembly quantity ofelectrolytic water to the component water; and reducing, responsive tothe transferring step, the water concentration of the liquidelectrolyte.

Sometimes further, the component includes the anode electrode and thecathode electrode and wherein each the electrode contains an activematerial including a transition metal cyanide coordination compoundmaterial having a composition conforming to formula I, formula Iincluding AxPy[R(CN)6]z(H2O)n; wherein A represents an alkali cation andP and R each represent a multivalent transition metal cation; wherein0.5<z<1; and wherein x, y, and z are related based on electricalneutrality, x>0, y>0, z>0; and wherein n=6*(1−z)+mk, with n>0, with k=0to 4 identifying a set of states for the electrodes, and with 6*(1−z)identifying as a quantity of coordinated water of the compound material,and with each mk>0, each mk identifying as a quantity of interstitialwater of the compound material for one of the states of the electrodes,with each the quantity mk of interstitial water being equivalent to aweight percentage Mk=mk*WH2O/Wdry*100%, with WH2O being the molecularweight of water and Wdry being the molecular weight for the compositionof formula I excluding all of its water content, with M0 identifying asan as-synthesized set of properties for the electrode, with M1identifying as a pre-communication set of properties for the anodeelectrode, with M2 identifying as a pre-communication set of propertiesfor the cathode electrode, with M3 identifying as a post-communicationset of properties for the anode electrode, and with M4 identifying as apost-communication set of properties for the cathode electrode; andwherein the liquid electrolyte includes a polar organic solvent combinedwith an alkali metal salt and water having a water concentration, thewater concentration including a pre-communication water concentration c1and including a post-communication water concentration c2 and whereinc1>c2; wherein the as-synthesized set of properties includes M0 up to45% for formula I materials; wherein the M1 includes a value less thanabout 12% for formula I materials of the anode electrode with M1≤M3;wherein the M2 includes a value less than about 12% for formula Imaterials of the cathode electrode with M2≤M4; and wherein M3+M4>M1+M2.

Advantages of some of the embodiments include an allowance for areduction of production cost through a consolidation of separatedehydration processes for battery electrodes, electrolyte salts andelectrolyte solvents into one or two process steps in which only thebattery electrodes may be dehydrated. This is of particular advantage inusing electrolytes made with organic solvents such as acetonitrile assolvent, because the manufacture of acetonitrile uses water as a processmedium to isolate acetonitrile from its mixture with acrylonitrile, andfurther processing is needed to subsequently remove water from thusobtained acetonitrile. Furthermore, strict environmental humiditycontrol may only be needed during cell stacking operations and not inthe upstream process steps.

Any of the embodiments described herein may be used alone or togetherwith one another in any combination. Inventions encompassed within thisspecification may also include embodiments that are only partiallymentioned or alluded to or are not mentioned or alluded to at all inthis brief summary or in the abstract. Although various embodiments ofthe invention may have been motivated by various deficiencies with theprior art, which may be discussed or alluded to in one or more places inthe specification, the embodiments of the invention do not necessarilyaddress any of these deficiencies. In other words, different embodimentsof the invention may address different deficiencies that may bediscussed in the specification. Some embodiments may only partiallyaddress some deficiencies or just one deficiency that may be discussedin the specification, and some embodiments may not address any of thesedeficiencies.

Other features, benefits, and advantages of the present invention willbe apparent upon a review of the present disclosure, including thespecification, drawings, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures, in which like reference numerals refer toidentical or functionally-similar elements throughout the separate viewsand which are incorporated in and form a part of the specification,further illustrate the present invention and, together with the detaileddescription of the invention, serve to explain the principles of thepresent invention.

FIG. 1 illustrates a representative secondary electrochemical cellschematic having one or more TMCCC electrodes disposed in contact with acosolvent electrolyte as described herein;

FIG. 2 illustrates a unit cell of a TMCCC crystal structure;

FIG. 3 illustrates a process sequence for cell optimization by use ofone or more water absorbing TMCCC electrodes;

FIG. 4 illustrates a concept view of select electrochemical cellcomponents in an “as synthesized” state for water concentrations for anelectrode and an electrolyte;

FIG. 5 illustrates the concept view of FIG. 4 with water concentrationof an electrode adjusted from its as synthesized state illustrated inFIG. 4 ;

FIG. 6 illustrates the concept view of FIG. 5 with water concentrationsof the electrode and the electrolyte each changing by a transfer ofwater from the electrolyte to the electrode;

FIG. 7 illustrates a charge-discharge potential profile of a sodiummanganese iron hexacyanoferrate cathode electrode with optimizedinterstitial water content, showing three distinct reduction/oxidationpotentials for N-coordinated Fe^(2+/3+), C-coordinated Fe^(2+/3+) andN-coordinated Mn^(2+/3+);

FIG. 8 illustrates a differential capacity plot derived from thepotential profile in FIG. 7 ;

FIG. 9 illustrates charge-discharge profiles of cells with TMCCCelectrodes and electrolytes with varied water content;

FIG. 10 illustrates cell energy versus time during float testing; and

FIG. 11 illustrates cell capacity versus time during float testing.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention provide a system and methodoptimizing electrochemical cell manufacturing by reducingcommercialization costs, including reduction of electrolyte costs usedin their manufacturing. The following description is presented to enableone of ordinary skill in the art to make and use the invention and isprovided in the context of a patent application and its requirements.

Various modifications to the preferred embodiment and the genericprinciples and features described herein will be readily apparent tothose skilled in the art. Thus, the present invention is not intended tobe limited to the embodiment shown but is to be accorded the widestscope consistent with the principles and features described herein.

Definitions

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this general inventive conceptbelongs. It will be further understood that terms, such as those definedin commonly used dictionaries, should be interpreted as having a meaningthat is consistent with their meaning in the context of the relevant artand the present disclosure, and will not be interpreted in an idealizedor overly formal sense unless expressly so defined herein.

The following definitions apply to some of the aspects described withrespect to certain embodiments of the invention. These definitions maylikewise be expanded upon herein.

As used herein, the term “or” includes “and/or” and the term “and/or”includes any and all combinations of one or more of the associatedlisted items. Expressions such as “at least one of,” when preceding alist of elements, modify the entire list of elements and do not modifythe individual elements of the list.

As used herein, the singular terms “a,” “an,” and “the” include pluralreferents unless the context clearly dictates otherwise. Thus, forexample, reference to an object can include multiple objects unless thecontext clearly dictates otherwise.

Also, as used in the description herein and throughout the claims thatfollow, the meaning of “in” includes “in” and “on” unless the contextclearly dictates otherwise. It will be understood that when an elementis referred to as being “on” another element, it can be directly on theother element or intervening elements may be present therebetween. Incontrast, when an element is referred to as being “directly on” anotherelement, there are no intervening elements present.

As used herein, the term “set” refers to a collection of one or moreobjects. Thus, for example, a set of objects can include a single objector multiple objects. Objects of a set also can be referred to as membersof the set. Objects of a set can be the same or different. In someinstances, objects of a set can share one or more common properties.

As used herein, the term “adjacent” refers to being near or adjoining.Adjacent objects can be spaced apart from one another or can be inactual or direct contact with one another. In some instances, adjacentobjects can be coupled to one another or can be formed integrally withone another.

As used herein, the terms “connect,” “connected,” and “connecting” referto a direct attachment or link. Connected objects have no or nosubstantial intermediary object or set of objects, as the contextindicates.

As used herein, the terms “couple,” “coupled,” and “coupling” refer toan operational connection or linking. Coupled objects can be directlyconnected to one another or can be indirectly connected to one another,such as via an intermediary set of objects.

The use of the term “about” applies to all numeric values, whether ornot explicitly indicated. This term generally refers to a range ofnumbers that one of ordinary skill in the art would consider as areasonable amount of deviation to the recited numeric values (i.e.,having the equivalent function or result). For example, this term can beconstrued as including a deviation of ±10 percent of the given numericvalue provided such a deviation does not alter the end function orresult of the value. Therefore, a value of about 1% can be construed tobe a range from 0.9% to 1.1%.

As used herein, the terms “substantially” and “substantial” refer to aconsiderable degree or extent. When used in conjunction with an event orcircumstance, the terms can refer to instances in which the event orcircumstance occurs precisely as well as instances in which the event orcircumstance occurs to a close approximation, such as accounting fortypical tolerance levels or variability of the embodiments describedherein.

As used herein, the terms “optional” and “optionally” mean that thesubsequently described event or circumstance may or may not occur andthat the description includes instances where the event or circumstanceoccurs and instances in which it does not.

As used herein, the term “size” refers to a characteristic dimension ofan object. Thus, for example, a size of an object that is spherical canrefer to a diameter of the object. In the case of an object that isnon-spherical, a size of the non-spherical object can refer to adiameter of a corresponding spherical object, where the correspondingspherical object exhibits or has a particular set of derivable ormeasurable properties that are substantially the same as those of thenon-spherical object. Thus, for example, a size of a non-sphericalobject can refer to a diameter of a corresponding spherical object thatexhibits light scattering or other properties that are substantially thesame as those of the non-spherical object. Alternatively, or inconjunction, a size of a non-spherical object can refer to an average ofvarious orthogonal dimensions of the object. Thus, for example, a sizeof an object that is a spheroidal can refer to an average of a majoraxis and a minor axis of the object. When referring to a set of objectsas having a particular size, it is contemplated that the objects canhave a distribution of sizes around the particular size. Thus, as usedherein, a size of a set of objects can refer to a typical size of adistribution of sizes, such as an average size, a median size, or a peaksize.

As used herein, the term “residual water content” of a coordinationcompound, particularly a TMCCC material, refers to a total water contentof the TMCCC. Residual water content includes a total water mass dividedby a total dry mass of the TMCCC material (the mass of the metals, CNgroups, and any other chemical species such as chelating species). Forexample, in the case of a TMCCC with a dry mass of 100 g and a totalwater content of 10 g, then the residual water content is calculated as10 g water/100 g dry mass=10%.

As used herein, a water content of a class of coordination compoundmaterials is a complex topic and refers to a hybrid residual water statewhich identifies a coordinated water content (e.g., coordinated water)and a non-coordinated water content (e.g., non-coordinated water).Non-coordinated water may be present in various ways, primarily asinterstitial water and/or water bound to surfaces of particles of thecoordination compound materials and/or water present in any pores ormicropores within a TMCCC particle. As used herein, “coordinated water”is meant as an abbreviated term for “transition metal-coordinated water”and, as such, specifically describes water molecules that coordinate totransition metal atoms, and not to alkali metal ions. While theinteraction between water and alkali metal ions could generally also beunderstood as “coordinated”, water molecules that interact with alkaliions and not with transition metal atoms are considered herein, due totheir relatively weak interaction, as belonging to the category ofnon-coordinated water. Coordinated water molecules are strongly bound totransition metal atoms that are deficient in cyanide ligands; therefore,coordinated water is considered essential for stabilizing TMCCCmaterials. Non-coordinated water above a threshold included in anoptimally selected residual water content would be considered anundesired impurity that degrades the desired electrochemical properties.However, removing all non-coordinated water may result in poor alkalication mobility in the TMCCC material, leading to diminished cell energyavailable for high-power discharge, with only marginal improvement ofcycle or calendar life of the cell. Therefore, in addition tocoordinated water, a certain amount of non-coordinated water is alsonecessary and desired. As discussed herein, absent sufficient care,water management processes (e.g., drying) may not sufficientlydistinguish between coordinated and non-coordinated water in a compoundcoordination material. Coordination compound materials discussed hereinmay be used in a system including a water-containing electrolyte whichmay influence the water content of the coordination compound materialafter assembly or during use. A coordination compound having itsresidual water adjusted to a desired non-degrading water content rangeis referred to herein as a water mediated coordination compoundmaterial. Similarly, a coordination compound having its residual wateroutside this range is referred to herein as a water non-mediatedcoordination compound material.

As used herein, the term “aqueous” in the context of an electrolyte foran electrochemical cell means an electrolyte including water as asolvent and one or more dissolved materials with the water solventhaving a concentration greater than 5%.

As used herein, the term “non-aqueous” in the context of an electrolytefor an electrochemical cell means an electrolyte including a solventother than water, with either no water being present or water having aconcentration less than 5%.

As used herein, the term “anhydrous” in the context of an electrolytefor an electrochemical cell means an electrolyte including a solventother than water, water as a trace impurity having a concentration lessthan 0.01%.

As used herein, the term “drying” in the context of removal of waterfrom a material, refers to removal of water to the greatest degreepossible consistent with the drying process leaving water as a traceimpurity at a concentration limited by the drying process actually used.Drying changes a material to an anhydrous state (therefore a driedmaterial is an anhydrous material).

As used herein, the term “dehydrating” in the context of modifying aconcentration of water in a material, refers to controllably reducingthe water content to a desired level greater than a trace impurity. Incontrast to drying, dehydrating contemplates retaining water asnecessary desirable component of the material, for example, retainingall coordinated water and retaining a certain residual content ofnon-coordinated water.

As used herein, the term “hydrating” in the context of modifying aconcentration of water in a material, refers to controllably increasingthe water content to a desired level greater than a trace impurity,within target ranges needed for optimal performance and calendar life ofan electrochemical cell.

As used herein, the term “mediating” in the context of modifying aconcentration of water content in a coordination compound such as aTMCCC material includes dehydrating or hydrating the material to achievea desired coordinated water concentration that enables the desiredelectrochemical properties. One way to consider water content quantitymediation is consideration of a mass fraction of water of a TMCCCmaterial, including non-coordinated and coordinated water, both beforeand after mediation.

Described herein is a new class of battery cell that is based onelectrodes that contain transition metal cyanide coordination compound(TMCCC) materials as electrochemically active materials. These TMCCCmaterials naturally contain water. Some of the water they contain istightly bound to transition metal atoms within the crystal structure ofthe material, whereas non-coordinated water is less strongly bound as itresides in interstitial sites, or at the surface of the TMCCC material.Some of the non-coordinated water may reversibly move in and out of theelectrode as it is charged and discharged. Water that leaves the TMCCCmaterial may then undergo chemical or electrochemical reactions withother cell components and thereby cause degradation of cell performance.One would therefore expect that continued removal of non-coordinatedwater from the TMCCC material would continue to enhance electrode andcell performance by eliminating these undesirable reactions. However, wefound that dehydration is beneficial only to a certain extent, beyondwhich it degrades the performance of the material. Embodiments of thepresent invention set the water content to a preferred level thatretains not only all of the coordinated water, but also a substantialcontent of non-coordinated water.

An alternative to electrochemical cells as described herein, and methodsfor their assembly and use, predetermine desired levels of water in thecomponents. Water impurities in electrolytes for battery cells can beeliminated by minimizing the water content of electrolyte components,and minimizing the exposure of these components to ambient humidityduring the process steps of mixing electrolyte solutions, storage,transport, and filling battery cells with electrolyte.

A disadvantage of this alternative includes use of additional processsteps such as vacuum-drying of electrolyte salts, drying electrolytesolvents over desiccants, regenerating the desiccant and avoidingimpurities introduced by the contact between solvent and desiccant, arecostly and may require additional downstream process modifications, suchas handling dried salts and solvents in gloveboxes or dry rooms that areexpensive to operate. Further, the purchase of materials that have beenprocessed this way require a premium charge over purchase of materialsthat offer less rigorous manufacturing, handling, and end-userequirements.

In contrast, use of an embodiment of the present invention may allow fora reduction of production cost through the consolidation of separatedehydration processes for battery electrodes, electrolyte salts andelectrolyte solvents into one or two process steps in which only thebattery electrodes are dehydrated. This may be of particular advantagein using electrolytes made with organic solvents such as acetonitrile assolvent, because the manufacture of acetonitrile uses water as a processmedium to isolate acetonitrile from its mixture with acrylonitrile, andfurther processing is needed to subsequently remove water from thusobtained acetonitrile. Furthermore, strict environmental humiditycontrol is typically only needed during cell stacking operations and notin the upstream process steps.

Some of the content described herein is generally related to U.S. patentapplication Ser. No. 16/708,213, the contents of which are herebyexpressly incorporated by reference thereto in its entirety for allpurposes. One embodiment of an electrochemical cell of concern includesa TMCCC anode and a TMCCC cathode, and a liquid electrolyte electricallycommunicated to the electrodes. This liquid electrolyte is made with oneor more organic solvents and at least one alkali metal salt, and may ormay not contain additives. Preferred examples of solvents includeacetonitrile, propionitrile, and butyronitrile for example. Preferredexamples of alkali metal salts include suitable salts containing analkali metal cation and an anion, wherein the alkali metal cation issodium, potassium, rubidium or cesium, and anions include, but are notlimited to, perchlorate, tetrafluoroborate, hexafluorophosphate,difluoro-oxalatoborate, triflate, bis(trifluoromethanesulfonyl)imide,bis(fluorosulfonyl)imide, dicyanamide, tricyanomethanide, and mixturesthereof. Preferred examples of sodium salts include sodium salts suchas, but not limited to, sodium perchlorate, sodium tetrafluoroborate,sodium hexafluorophosphate, sodium difluoro-oxalatoborate, sodiumtriflate, sodium bis(trifluoromethanesulfonyl)imide, sodium dicyanamide,and sodium tricyanomethanide, and mixtures thereof. A preferred sodiumsalt includes sodium bis(trifluoromethanesulfonyl)imide. Examples ofadditives include malonitrile, succinonitrile, glutaronitrile, andadiponitrile with a mass ratio between solvent and additive between 99:1and 70:30.

FIG. 1 illustrates a representative secondary electrochemical cell 100schematic having one or more TMCCC electrodes disposed in contact with acosolvent electrolyte as described herein. Cell 100 includes a negativeelectrode 105, a positive electrode 110 and an electrolyte 115electrically communicated to the electrodes.

FIG. 2 illustrates a unit cell of the cubic Prussian Blue crystalstructure, one example of a TMCCC structure. Transition metal cationsare linked in a face-centered cubic framework by cyanide bridgingligands. The large, interstitial A sites can contain water and/orinserted alkali ions.

FIG. 3 illustrates a process sequence 300 for cell optimization by useof one or more water absorbing TMCCC electrodes including steps 305-315.In step 305, desired components of an electrochemical cell are obtained,such as through manufacture or purchase. For simplifying thediscussions, two components of a cell stack for a secondaryelectrochemical cell including TMCCC active materials are described inprocess 305. These components include an electrode and an electrolyte.Further, this example scenario includes a chemical manufacturersynthesizing TMCCC active materials for the electrode and a third-partymanufacturer producing an electrolyte to be used with the electrode andother components such as additional electrodes, binders, separators,additives, and the like. The TMCCC active material to be included inthis electrode includes an “as synthesized” quantity of water that maybe present in various forms, e.g., coordinated, interstitial, andsurface. The electrolyte used with such an electrode will include, forthis example, a combination of solvents, one of which is water whichexceeds a quantity more than a “trace” or “impurity” quantity asdiscussed herein.

Step 310 includes pre-assembly processing of one or more components ofthe electrochemical (that is, before the electrodes are communicated tothe electrolyte and other assembly of the final electrochemical cell areproduced). In this example, the electrode is pre-processed to removesome of the as-synthesized water. In some cases, the water concentrationof the electrode may be set or determined to a desired/acceptable levelduring synthesis so that a separate distinct step of adjusting the waterconcentration is not required.

Step 315 assembles the electrochemical cell from the components,including those that have been pre-processed. Some or all of thecomponents of the cell have different water concentrations post-assemblyfrom their pre-assembly water concentrations. For this example, waterfrom the electrolyte is transferred to the water-reduced TMCCCelectrode. This transfer results in the water concentration of theelectrolyte decreasing and the water concentration in the electrodeincreasing during step 315.

FIG. 4 -FIG. 6 illustrate a result of the process 300 in the context ofone electrode and a simple electrolyte and that other implementationsare possible as described herein. FIG. 4 illustrates a concept view ofselect components of an electrochemical cell 400 in an “as synthesized”state for water concentrations for an electrode and an electrolyte.These components include a TMCCC electrode 405 and a quantity ofelectrolyte 410. The small circles represent water that is present inthe components.

FIG. 5 illustrates the concept view of FIG. 4 with a pre-assembly system500 including a pre-assembly processing of electrode 405 of FIG. 4 toadjust it so that it is a water-adjusted (reduced) electrode 505 whereinthe water concentration of electrode 405 is reduced from its assynthesized state. The fewer number of visualized small circles inelectrode 505 of FIG. 5 represent this decreased water concentration forelectrode 505 as compared to electrode 405 of FIG. 4 .

FIG. 6 illustrates the concept view of FIG. 5 with a post-assemblysystem 600 including a post-assembly change in water concentrations of apost-assembly electrode 605 and a post-assembly electrolyte 610. Asillustrated by the change in the number of small circles in electrode605, a water concentration of electrode 605 is greater than pre-assemblyelectrode 505 (and may be more, less, or the same as the waterconcentration of as-synthesized electrode 405). Similarly, a waterconcentration of post-assembly electrolyte 610 is less than the waterconcentration of electrolyte 410 which in this example was obtained froma third party. These changes of water concentrations in system 600include a transfer of water from electrolyte 410 to electrode 505 toproduce the concentrations represented by FIG. 6 .

TMCCC anodes and TMCCC cathodes used in a secondary electrochemical cellmay be made in a precipitation reaction by mixing precursor solutions inwater of transition metal salts, alkali metal salts, and either alkalicyanide or hexacyanometallate salts; examples of said precipitationreaction can be found in US 2020/0071175 A1, expressly incorporated byreference thereto in its entirety.

The as-synthesized materials typically contain substantial amounts ofwater that exists in three different forms: (i) water moleculesphysisorbed to the surface of TMCCC particles, (ii) water molecules ininterstitial spaces of a regular TMCCC crystal lattice, and (iii) watermolecules coordinated to transition metal sites with an incompletecoordination environment due to an adjacent hexacyanometallate vacancy.For each hexacyanometallate vacancy present in the TMCCC lattice, thesix neighboring transition metal sites each lack one of six cyanideligands; each of these transition metal sites then coordinates to onewater molecule, thus maintaining a sixfold coordination environment. Inthe following, these three forms of water in (i)-(iii) may be referredto as (i) surface water, (ii) interstitial water, and (iii) coordinatedwater.

Typical non-coordinated water contents of TMCCC materials in theiras-synthesized form can range from about zero to about 45% by anhydrousweight. The water content of synthesized TMCCC electrodes in an exampleelectrochemical cell may be reduced by vacuum drying; however, thevacuum drying process is intentionally carried out in such a way that astill substantial amount of non-coordinated water is retained in theelectrode materials, which typically is within a range from 1% to 12%.

It is important to note there are several differences betweencompositions of matter disclosed in incorporated references US2019/0190006 A1 and U.S. Pat. No. 9,099,718 B2, and the electrodecompositions of matter described herein. In references US 2019/0190006A1 and [2], cathode electrodes are dehydrated to the extent that all oftheir initial water content is removed with the exception of coordinatedwater, for example. By contrast, the residual water content in the TMCCCelectrodes described herein is not limited to coordinated water, but asubstantial amount of interstitial water is also retained. Typicalpartially dehydrated anodes in the battery cell described herein containonly between 0.7% to 5% residual water content as coordinated water,whereas the remaining portion, typically the majority, is in the form ofinterstitial water. Likewise, typical partially dehydrated cathodesdescribed herein contain only between 4% and 6% (wt.) residual watercontent in the form of coordinated water, and an additional 0.5% to 5%of interstitial water is still present. The true amount of interstitialwater can be expected to be even larger than the aforementioned valueswhen the total water content is underreported by a Karl Fischertitration, whose accuracy relies on all of the water content beingreleased upon heating. Heat-induced reactions that consume water, suchas formation of metal oxides and hydrogen gas, are not uncommon inmeasurements of water content in solid materials, and lead toartificially lower readings in a Karl Fischer titration. Furthermore,reference [2] describes a TMCCC cathode materialA_(x)Mn[Fe(CN)₆]_(y).zH₂O in which the removal of interstitial water hascaused the material to form a rhombohedral crystal structure, withMn^(2+/3+) and Fe^(2+/3+) having the same reduction/oxidation potential.By contrast, our invention includes TMCCC materials having the samecrystal structure in their as-synthesized and in their partiallydehydrated forms, and it also includes TMCCC cathode materials having acubic crystal structure and having three different oxidation-reductionpotentials for nitrogen-coordinated Fe^(2+/3+), carbon-coordinatedFe^(2+/3+), and nitrogen-coordinated Mn^(2+/3+). As an example, FIG. 7shows a charge-discharge potential profile of a sodium iron manganesehexacyanoferrate electrode having a cubic crystal structure, which wasdehydrated from an as-synthesized water content of 17% to a residualwater content of 7.3%. Three distinct oxidation/reduction potentials arefound at 2.95 V, 3.37 V and 3.6 V, respectively. FIG. 8 shows thedifferential capacity plot that is derived from the potential profile inFIG. 7 . In comparing the composition of matter with the specificcapacity at each of the three oxidation/reduction potentials, we foundthat the capacity measurements are in perfect agreement with anassignment the three redox potentials as nitrogen-coordinated Fe^(2+/3+)(2.95 V), carbon-coordinated Fe^(2+/3+) (3.37 V) andnitrogen-coordinated Mn^(2+/3+) (3.6 V). An advantage of thiscomposition of matter over a fully anhydrous sodium iron manganesehexacyanoferrate electrode having the same composition of matter exceptfor its water content is that the presence of interstitial water notonly prevents the formation of the rhombohedral structure, but it alsomaintains the cubic crystal structure of the electrode materialthroughout its entire range of sodium intercalation/deintercalation. Oneskilled in the art will recognize the advantages of an electrodematerial exhibiting solid-solution intercalation mechanism instead of aphase-change mechanism, where the former mechanism typically results inhigher rate capability and longer cycle life. Furthermore, the presenceof multiple reactions is desirable because it allows for differentialcoulometry techniques that enable more precise state of charge and stateof health monitoring.

These partially dehydrated TMCCC electrodes may act as strong desiccantswith substantial water absorption capacity when in contact withorganic-solvent-based electrolytes that contain water as an impurity.Other materials systems that are known to intercalate water, such aszeolitic metal oxides, reach an equilibrium between interstitial waterand ambient water in an electrolyte. That equilibrium can be describedwith a Langmuir isotherm or, if a distribution of absorption energiesinto non-equivalent sites is present, a convolution of several differentLangmuir isotherms, similar to what has been reported for the waterabsorption of zeolite materials (R. Lin, A. Ladshaw, Y. Nan, J. Liu, S.Yiacoumi, C. Tsouris, D. W. DePaoli, and L. L. Tavlarides, Ind. Eng.Chem. Res. 2015, 54, 42, 10442-10448).

Generally, the distribution of water between its states of beingdissolved in the electrolyte and being absorbed in the anode and/orcathode active material can be described with a mass-balance equation:m _(H2O) ^(cell) =x ₀ m _(E) +y ₀ m _(C) +z ₀ m _(A) =x ₁ m _(E) +y ₁ m_(C) +z ₁ m _(A)  (I)

wherein m_(H2O) ^(cell) is the total water content of all cellcomponents, m_(E), m_(C) and m_(A) are the masses of electrolyte,cathode active material and anode active material, respectively, x_(i),y_(i) and z_(i) are the mass fractions of water in the electrolyte, thecathode active material and the anode active material, respectively, andthe indices 0 and 1 refer to the initial and final distribution ofwater, such that index 0 describes a distribution in which anelectrolyte with a higher water content x₀ is filled into a cellcontaining a stack of cathode and anode electrodes, wherein the cathodeelectrodes have been partially dehydrated to an initial residual watercontent y₀ and the anode electrodes have been partially dehydrated to aninitial residual water content z₀. Upon equilibration between the cellcomponents, water is redistributed, resulting in the distributions ofx₁, y₁ and z₁. This equilibrium is spontaneously reached under astandard cell filling procedure in which electrolyte is added to theelectrode stack, after which the cell pouch is heat-sealed and storedfor a duration of hours.

Upon said redistribution of water from the cell electrolyte to theelectrode active materials, the electrolyte water content is diminishedby

$\begin{matrix}{{\Delta x} = {{x_{1} - x_{0}} = {- \frac{{\Delta ym_{C}} + {\Delta zm_{A}}}{m_{E}}}}} & ({II})\end{matrix}$

In a typical cell design, the electrolyte volume is optimized in such away that the porous structure of the cell stack is wetted, and porevolume and electrolyte volume are optimized to achieve high power, highenergy density and long cycle life. Generally, the masses of activematerials and electrolyte can be expected to be of the same or verysimilar order of magnitude. Since TMCCC electrodes can contain severalpercent by weight of interstitial water at equilibrium with electrolytecontaining only trace impurities of water, very large values of Δx canbe achieved.

A preferred multi-layer pouch cell design with 4.5 Ah capacity containsapproximately 62 g (by anhydrous mass) TMCCC anode active material,between 61 g and 70 g (by anhydrous mass) TMCCC cathode active material,and approximately 59 g liquid electrolyte. The electrolyte in saidpreferred cell design may contain up to 1000 ppm water by weight as animpurity (x₀); such water impurity may be introduced with one or more ofthe electrolyte components (electrolyte salt, solvents, additives)and/or with the process conditions of mixing the electrolyte, duringwhich electrolyte salts, solvents, additives and/or their mixture may beexposed to a humid atmosphere. In said cell design with a cathode activematerial to electrolyte weight ratio between 1.05 and 1.2, the watercontent of electrolyte initially containing up to 1000 ppm water isdiminished to 20 ppm or less upon contact with the cathode (x₁), with 20ppm being the detection limit for water using Karl Fischer titration,whereas the water content of the cathode active material increases by nomore than 800 ppm (Δy). Since the preferred total residual water contentof an active material (y₁ or z₁) is between 6% and 9%, and the additionof less than 0.1% has no measurable effect on cell performance or cyclelife, such a wide range of water impurities in the electrolyte as from 0ppm up to 1000 ppm can be tolerated without needing to adjust theprocess conditions for dehydration of anode or cathode electrodes. Thisprinciple may be further extended to include an initial electrolytewater concentration x₀ of greater than 1000 ppm, and in someembodiments, of approximately 50,000 ppm, while still achieving apreferred final water distribution x₁, y₁, z₁.

The said function of TMCCC electrode materials as a desiccant is notlimited to one particular composition of matter of a TMCCC material, butit can be achieved with any TMCCC cathode or anode material that has asubstantial affinity towards absorption of interstitial water. Preferredexamples of such interstitially hydrated TMCCC materials includehexacyanoferrates including but not limited to sodium manganese ironhexacyanoferrates, sodium iron hexacyanoferrates, sodium manganesehexacyanoferrates, sodium copper hexacyanoferrates, sodium nickelhexacyanoferrates, potassium nickel hexacyanoferrates,hexacyanomanganates including but not limited to sodium manganesehexacyanomanganates and sodium zinc hexacyanomanganates, andhexacyanochromates including but not limited to sodium manganesehexacyanochromate. Particularly preferred cathode TMCCC materials aresodium manganese iron hexacyanoferrates with a compositionNa_(2−s−p(4−s)q)Mn^(II) _(1−p)Fe^(III)_(p)[Fe^(II+s)(CN)₆]_(1−q)(H₂O)_(6q+r), wherein 0≤p≤1, 0<q≤0.5, r≥0, and0≤s≤1. Particularly preferred anode TMCCC materials are sodium manganesehexacyanomanganates with a compositionNa_(2−4q)Mn[Mn(CN)₆]_(1−q)(H₂O)_(6q+r), wherein 0≤q≤0.5 and r≥0.

In another preferred cell design, an electrolyte with even higher watercontent on the order of several percent can be used, when thedehydration process for the electrodes is adjusted accordingly to avoidhigher than preferred total water content of the cell. In this case, oneor both of the anode and cathode electrodes is initially dehydrated to aresidual water content that is intentionally lower than the watercontent that is targeted for optimal cell performance. Said optimumwater concentrations in the electrode active materials are then gainedback upon exposure of the “over-dried” electrode stack to theelectrolyte.

In one preferred cell design, a TMCCC cathode is used and the optimumresidual water content in said TMCCC cathode is 6.4%, of which 4.8%water is present as coordinated water and 1.6% is present asinterstitial water, the anode in this cell design is dehydrated to anoptimum residual water content of 7.5%, the TMCCC cathode is over-driedto 5.3% residual water content and electrolyte with an initial watercontent of 12,000 ppm is used.

In another preferred cell design, the TMCCC cathode is used anddehydrated to its optimum residual water content of 6.4%, and a TMCCCanode, containing 2.2% coordinated water and, for optimum cellperformance and cycle life, 5.4% interstitial water, is dehydrated to3.1% residual water content, and the resulting cell is filled withelectrolyte containing 42,000 ppm water.

Many other variations of this type of cell design can be practiced, inwhich electrolytes with substantial initial water content, ranging up to50,000 ppm, can be effectively desiccated when appropriate TMCCCelectrode materials with low initial water content and large waterabsorption capacity are employed.

In addition, variations of this type of cell design could incorporateone or electrodes each of which comprising a combination of one or moreTMCCC materials and another electrochemically active electrode material.In such a variation, said one or more TMCCC materials could beintroduced as a component to the electrode in a concentration of 1% to10% or more, and said electrodes may contain another electrochemicallyactive electrode material including but not limited to carbons such asgraphite or hard carbon, metallic and intermetallics such as sulfur andsilicon, or ceramics such as transition metal oxides or phosphates,including but not limited to lithium transition metal oxides such aslithium cobalt oxide, lithium manganese oxide, or lithium nickel cobaltmanganese oxide, or lithium transition metal phosphates such as lithiumiron phosphate, and including but not limited to sodium transition metaloxides or phosphates, including but not limited to sodium titaniumphosphate and oxides containing sodium, nickel, and optionally one ormore other transition metals. In such as variation, the TMCCC componentof said electrode would absorb water from the electrolyte as describedherein, enhancing the performance of the cell or said anotherelectrochemically active electrode material.

Example 1: Karl Fischer Titration of Electrolytes Before and AfterContact with TMCCC Cathode

Three electrolytes with a concentration of 0.88 M NaTFSI in acetonitrileand with a systematic variation of water content were made, referred tohereafter as electrolytes a, b and c. Electrolyte a was taken from astock solution made with high-purity acetonitrile and NaTFSI salt,whereas electrolytes b and c were made by intentionally adding smallamounts of water to aliquots taken from electrolyte a, in order toobtain target water concentrations of 500 ppm and 1000 ppm inelectrolytes b and c, respectively.

Each of the electrolytes a, b and c was exposed to a partiallydehydrated TMCCC cathode. For this purpose, cathode electrodes made withhydrated sodium manganese iron hexacyanoferrate as the active material,with an active material mass loading of approximately 15.3 mg/cm² byanhydrous active material weight, an area of approximately 385 cm²,calendared to a porosity of approximately 35%, were vacuum-dried to aresidual water content of 7.2%±0.1% by active material weight.

For each electrolyte exposure test, one of the said cathode electrodeswas placed inside a laminated aluminum pouch, and a volume ofelectrolyte twice as large as the pore volume of the electrode wasadded. The pouches were then heat-sealed and stored overnight, afterwhich they were cut open and the excess electrolyte volume collected forKarl Fischer titration.

Table 1 illustrates the measured water content in electrolytes a, b andc before and after exposure to partially dehydrated cathode electrodes.Illustrated is a desiccant effect of sodium manganese ironhexacyanoferrate cathodes in contact with 0.88 M NaTFSI/acetonitrileelectrolytes with different initial water concentrations. ElectrolyteH₂O concentrations before and after exposure are measured by KarlFischer titration; the H₂O absorption of the cathode samples iscalculated from the H₂O concentration change in the electrolyte. In eachof the three electrolyte samples, regardless of their initial watercontent, the water content after exposure was diminished to thedetection limit of the Karl Fischer titration.

TABLE 1 Desiccant effect H₂O before H₂O after Calculated cathodeexposure to exposure to H₂O absorption Electrolyte cathode (ppm) cathode(ppm) (% wt. of active) a 59 16 0.005 b 491 23 0.05 c 1009 22 0.09

Example 2: Karl Fischer Titration of Electrolytes Before and AfterContact with TMCCC Anode

Three electrolytes with a concentration of 0.88 M NaTFSI in acetonitrileand with a systematic variation of water content were made, referred tohereafter as electrolytes d, e and f. The electrolytes were made usingthe same procedure as for electrolyte a in Example 1, followed byadditions of small amounts of water in order to reach target waterconcentrations of 100 ppm, 1000 ppm and 10000 ppm, respectively. Each ofthe electrolytes d, e and f was exposed to a partially dehydrated TMCCCanode. In addition to electrolyte exposure to partially dehydratedanodes directly obtained from the vacuum-drying process, the effect ofanode SOC was also tested.

Anode electrodes made with hydrated sodium manganese hexacyanomanganateas the active material, with an active material mass loading ofapproximately 14.8 mg/cm², an area of approximately 385 cm², calendaredto a porosity of approximately 28%, were vacuum-dried to a residualwater content of 7.5%.

Three anodes with an SOC of 0% were directly obtained from thevacuum-drying process and exposed to electrolytes d, e, and f using thesame procedure as in Example 1. Additional anodes from the same dryingbatch were built into multilayer pouch cells using sodium manganese ironhexacyanoferrate cathodes with 6.8% cathode residual water content.These cells underwent 1C-1C charge-discharge cycles and were stopped atappropriate voltages to obtain anode SOCs of 50%, 80% and 100%,respectively. The thus prepared anodes were harvested from their cellsand subjected to the same soaking protocol as the 0% SOC anodes.

Table 2 illustrates an electrolyte water content in electrolytes d, eand f before and after exposure to partially dehydrated anodes at fourdifferent anode states of charge. At the given initial residual watercontent of 7.5% in the anode, the corresponding equilibrium waterconcentration in the electrolyte is 128 ppm. While this indicates alower affinity of the anode material towards water absorption, we stillobserve substantial removal of water from electrolytes with higherinitial concentrations of 1017 and 9983 ppm. It is noteworthy that theanode in this example has a much higher initial concentration ofinterstitial water (6.5%) prior to electrolyte exposure than the cathodein Example 1 (2.4%), and still exhibits substantial absorption capacity.An additional benefit can be seen in Table 2, which illustrates that thestate of charge of this electrode material does not significantly affectits water absorption capacity, allowing the cell to be assembled at anystate of charge while still retaining the ability to capture water froman electrolyte. Described is a desiccant effect of sodium manganesehexacyanomanganate anodes at different SOCs in contact with 0.88 MNaTFSI/acetonitrile electrolytes with initial water concentrations.Electrolyte H₂O concentrations before and after exposure are measured byKarl Fischer titration; the H₂O absorption of the anode samples iscalculated from the H₂O concentration change in the electrolyte.

TABLE 2 Desiccant effect Anode H₂O before H₂O after Calculated anode SOCexposure to exposure to H₂O absorption Electrolyte (%) anode (ppm) anode(ppm) (% wt. of active) d 0 128 98 0.003 d 50 128 128 0.000 d 80 128 1300.000 d 100 128 128 0.000 e 0 1017 134 0.09 e 50 1017 172 0.07 e 80 1017213 0.07 e 100 1017 236 0.07 f 0 9983 1730 0.72 f 50 9983 1429 0.75 f 809983 1919 0.70 f 100 9983 1876 0.71

Example 3: Cell Design with Electrolytes Containing Different WaterImpurity Levels

Cathode electrodes made with hydrated sodium manganese ironhexacyanoferrate were partially dehydrated to a residual water contentof 7.1%±0.1% using the same vacuum drying process as in example 1. Anodeelectrodes made with hydrated sodium manganese hexacyanomanganate as theactive material, with an active material mass loading of approximately14.8 mg/cm² and an electrode porosity of approximately 28%, werevacuum-dried for 70 minutes at 80° C. to a residual water content of7.8%±0.1%. Anode and cathode electrodes were stacked and formed intomulti-layer pouch cells. Three different groups A, B and C of cells weremade with different electrolytes. The electrolytes used in cell groupsA, B and C had the same compositions as the electrolytes a, b and c inexample 1, respectively. All three groups of cells were subjected to anaccelerated cycle age test at 45° C., during which they werecontinuously floated at a maximum voltage of 1.81 V and fully dischargedat a 2.2C rate once daily.

FIG. 9 illustrates the initial 1C-1C voltage profiles of cells fromgroups A, B and C.

FIG. 10 illustrates the cell energy versus time for cells from groups A,B, and C, measured during the accelerated cycle age test at 45° C.

FIG. 11 illustrates the cell capacity versus time for cells from groupsA, B, and C, measured during the accelerated cycle age test at 45° C.

No differences were observed between the initial 1C-1C voltage profilesof cells with varied electrolyte water content, and during 3 months ofaccelerated cycle-aging the performance of the three different groupswas indistinguishable in terms of energy fade and capacity fade. Theseobservations are consistent with the desiccant property of the cathodematerial demonstrated in Example 1. The added water in the 491 ppm and1009 ppm groups is entirely absorbed by the cathode, and the differencesin resulting cathode water introduced with the electrolyte are less than0.09% between the groups; these differences are within typical processvariations of electrode vacuum drying and their effect on cellperformance or cell life are negligible.

REFERENCES—EXPRESSLY INCORPORATED HEREIN BY REFERENCE THERETO

-   Reference [1]—Imhof, R. In Situ Investigation of the Electrochemical    Reduction of Carbonate Electrolyte Solutions at Graphite    Electrodes. J. Electrochem. Soc., 145, 1081-1087 (1998)-   Reference [2]—U.S. Pat. No. 9,099,718 B2 (Lu '718)-   Reference [3]—Wu, J, et al, J. Am. Chem. Soc., 139, 18358-18364    (2017),

The system and methods above have been described in general terms as anaid to understanding details of preferred embodiments of the presentinvention. In the description herein, numerous specific details areprovided, such as examples of components and/or methods, to provide athorough understanding of embodiments of the present invention. Somefeatures and benefits of the present invention are realized in suchmodes and are not required in every case. One skilled in the relevantart will recognize, however, that an embodiment of the invention can bepracticed without one or more of the specific details, or with otherapparatus, systems, assemblies, methods, components, materials, parts,and/or the like. In other instances, well-known structures, materials,or operations are not specifically shown or described in detail to avoidobscuring aspects of embodiments of the present invention.

Reference throughout this specification to “one embodiment”, “anembodiment”, or “a specific embodiment” means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment of the present invention and notnecessarily in all embodiments. Thus, respective appearances of thephrases “in one embodiment”, “in an embodiment”, or “in a specificembodiment” in various places throughout this specification are notnecessarily referring to the same embodiment. Furthermore, theparticular features, structures, or characteristics of any specificembodiment of the present invention may be combined in any suitablemanner with one or more other embodiments. It is to be understood thatother variations and modifications of the embodiments of the presentinvention described and illustrated herein are possible in light of theteachings herein and are to be considered as part of the spirit andscope of the present invention.

It will also be appreciated that one or more of the elements depicted inthe drawings/figures can also be implemented in a more separated orintegrated manner, or even removed or rendered as inoperable in certaincases, as is useful in accordance with a particular application.

Additionally, any signal arrows in the drawings/Figures should beconsidered only as exemplary, and not limiting, unless otherwisespecifically noted. Combinations of components or steps will also beconsidered as being noted, where terminology is foreseen as renderingthe ability to separate or combine is unclear.

The foregoing description of illustrated embodiments of the presentinvention, including what is described in the Abstract, is not intendedto be exhaustive or to limit the invention to the precise formsdisclosed herein. While specific embodiments of, and examples for, theinvention are described herein for illustrative purposes only, variousequivalent modifications are possible within the spirit and scope of thepresent invention, as those skilled in the relevant art will recognizeand appreciate. As indicated, these modifications may be made to thepresent invention in light of the foregoing description of illustratedembodiments of the present invention and are to be included within thespirit and scope of the present invention.

Thus, while the present invention has been described herein withreference to particular embodiments thereof, a latitude of modification,various changes and substitutions are intended in the foregoingdisclosures, and it will be appreciated that in some instances somefeatures of embodiments of the invention will be employed without acorresponding use of other features without departing from the scope andspirit of the invention as set forth. Therefore, many modifications maybe made to adapt a particular situation or material to the essentialscope and spirit of the present invention. It is intended that theinvention is not limited to the particular terms used in followingclaims and/or to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include any and all embodiments and equivalents falling within thescope of the appended claims. Thus, the scope of the invention is to bedetermined solely by the appended claims.

What is claimed as new and desired to be protected by Letters Patent ofthe United States is:
 1. A method for assembling an electrochemicalcell, comprising: a) a step of assembling a cell stack having a liquidelectrolyte, an anode electrode, a separator, and a cathode electrode,said electrodes electrochemically communicated with said liquidelectrolyte after said step of assembling a cell stack, with said cellstack having an as-synthesized set of properties, a pre-assembly set ofproperties before said electrodes are electrochemically communicatedwith said liquid electrolyte, and a post-assembly set of propertiesafter said electrodes are electrochemically communicated with saidliquid electrolyte; b) a step of transferring water, responsive to saidstep of assembling a cell stack, from said liquid electrolyte to atleast one of said electrodes; and c) a step of decreasing, responsive tosaid step of transferring water, a concentration of water in said liquidelectrolyte; wherein a first particular one electrode of said electrodesincludes a transition metal cyanide coordination compound materialhaving a composition conforming to formula I, formula I includingA_(x)P_(y)[R(CN)₆]_(z)(H₂O)_(n); wherein A represents an alkali cationand P and R each represent a multivalent transition metal cation;wherein 0.5<z<1; wherein x, y, and z are related based on electricalneutrality, x>0, y>0, z>0; and wherein n=6*(1−z)+m_(k), with n>0, withk=0 identifying an as-synthesized material and k=1 to 2 identifying aset of post-synthesized states for said first particular one electrode,and with 6*(1−z) identifying as a quantity of coordinated water of saidcompound material, and with each m_(k)>0, each m_(k) identifying as aquantity of interstitial water of said compound material for one of saidstates of said first particular one electrode, with each said quantitym_(k) of interstitial water being equivalent to a weight percentageM_(k)=m_(k)*W_(H2O)/W_(dry)*100%, with W_(H2O) being the molecularweight of water and W_(dry) being the molecular weight of saidcomposition conforming to formula I excluding all of its water content,with M₀ identifying as an as-synthesized set of properties for saidfirst particular one electrode, with M₁ identifying as apre-communication set of properties for said first particular oneelectrode, with M₂ identifying as a post-communication set of propertiesfor said first particular one electrode; and wherein said liquidelectrolyte includes a polar organic solvent combined with an alkalimetal salt and water having a water concentration, said waterconcentration including a pre-communication water concentration c1 andincluding a post-communication water concentration c2 and wherein c1>c2;wherein said as-synthesized set of properties includes M₀ up to 45% fora set of as-synthesized materials, said set of as-synthesized materialsincluding said composition conforming to formula I; wherein said M₁includes a range between 1% and 12% for a set of electrode materials ofsaid first particular one electrode, said set of electrode materialsincluding said composition conforming to formula I; and wherein M₂>M₁.2. The method of claim 1 wherein a second particular one electrode ofsaid electrodes different from said first particular one electrode doesnot include a transition metal cyanide coordination compound materialhaving a composition conforming to formula I.
 3. The method of claim 2wherein said first particular one electrode includes said anodeelectrode and wherein said second particular one electrode of saidelectrodes different from said first particular one electrode includessaid cathode electrode.
 4. The method of claim 2 wherein said firstparticular one electrode includes said cathode electrode and whereinsaid second particular one electrode of said electrodes different fromsaid first particular one electrode includes said anode electrode.